1. Field of the Invention
This invention relates to an electrolytic cell comprising a plurality of parallel anodes and cathodes which are closely spaced apart and have confronting surfaces.
2. Discussion of Prior Art
The electrolysis of alkali chloride solutions or acid alkali sulfate solutions to produce alkali chlorates or alkali persulfates is usually carried out in electrolytic cells having steel cathodes and titanium anodes. The anodes are usually provided with an activating coating, which consists, e.g., of mixed oxides of platinum metals. In the production of alkali chlorate by an electrolysis of alkali chloride solutions, the titanium of the anode serves to carry electric current and the presence of the activating coating reduces the voltage required for a deposition of chlorine so that energy is saved. The dimensions of the anode material are selected in dependence not only on the current density (kA/m.sup.2) but also of the distance to be traversed by the current in the anodes themselves. To ensure a uniform distribution of current over the anodes, the voltage drop in the anodes must be small compared with the voltage drop in the electrolyte. For this reason, the cross-sectional area of the anode material must be relatively large.
It is known to connect titanium anodes at the vertical housing walls of the electrolytic cell in such a manner that the total current is uniformly distributed over the several sheet electrodes and flows across the cell. When the anodes are connected to the cell walls, flanged anodes are commonly used, which are secured to the cell walls by connecting screws or welded joints. It is known from German Auslegeschrift 26 45 121 that current may be centrally fed to the anodes by means of a so-called center electrode consisting of a current-feeding pin provided on the vertical center line of the anodes. The length of the path along which the current must flow is thus reduced to one-half so that the thickness of the material can be reduced considerably or to one-half.
While affording this advantage and resulting in a suitable, compact structure, the previously known design involves considerable difficulties regarding the assembling of the anode set. Additionally, losses are involved in the flow of current from the copper pin over the female screw threads of the threaded sleeve and the male screw threads of the sleeve to the threaded rings. Each anode plate is individually and loosely fitted on current-feeding threaded sleeves and is fixed by means of individual threaded rings, which serve also as spacers. The electric contact is established by a pressure contact joint. This operation is repeated until the desired number of anode plates have been mounted. In that method, particularly high costs are due to the need for platinizing the contacting surfaces of the anode and of the threaded rings and the threaded sleeves carried by the current-feeding pins, in order to ensure that the voltage drop at the interfaces will always be low. In another embodiment of the known electrolytic cell, the current-feeding threaded sleeves may have annular ribs, which have the same thickness as the anode plates. The diameter of the ring only slightly exceeds the opening in the anode plate so that the ring is almost flush with the anode plate. That ring is fixed by a welded joint.
It is an object of the invention to eliminate the above-mentioned disadvantages and to provide for an electrolytic cell an anode assembly which can be assembled simply and in an economical manner.